This invention relates to improvements in collapsible steering column assemblies for vehicles that can collapse during a crash.
Steering column assemblies for automotive vehicles and the like are increasingly required to be adjustable for steering wheel height known as rake and, in many cases, steering wheel distance known as reach. This requires the column shroud, within which the steering column shaft attached to the steering wheel is rotatably located, to be fixed to the vehicle by a clamp mechanism which can be locked and unlocked to either prevent or permit adjustment of the column shroud position respectively.
A typical adjustable steering column assembly is constructed along the lines of the assembly shown in FIG. 1 of the drawings, and comprises a first shroud portion 100, a second shroud portion 200 and a clamp mechanism 300 that includes a support bracket 500 secured to a mounting bracket (not shown) which is in turn secured to a fixed part of a vehicle. Within the context of this description it should be understood that a mounting bracket will typically be fixed to, or form an integral part of, a Cross Car Beam (CCB) which runs from one side of a vehicle to the other forward of the driver behind the dashboard. The first and second portions 100, 200 are releasably engaged by the clamp mechanism 300 to selectively permit an amount of relative movement between the first and second portions that is required during adjustment of the steering column assembly. The clamp mechanism can be unlocked and locked by movement of a locking lever or handle or, sometimes, electrically using a motor or perhaps hydraulically or pneumatically. When the handle is unlocked it is possible to adjust the steering wheel ‘reach’ and “rake” position in & out only up to predetermined limits.
By releasing the clamp mechanism and telescopically sliding the first portion 100 over the second portion 200 the length of the shroud can be altered, altering the reach position of an associated steering wheel. By moving both portions together up and down relative to the clamp mechanism the rake can be adjusted. In some assemblies only one of reach and rake may be adjusted.
When the clamp mechanism is locked the length of the steering column assembly is fixed, and it is prevented from moving due to the rigid connection from the shroud, through the clamp mechanism to the rake bracket and on through the mounting bracket to the vehicle. In the event of a crash it is desirable for the steering column assembly to collapse in a controlled manner. This helps to reduce the forces of a driver colliding with the steering wheel or its airbag. In one known arrangement this controlled collapse is enabled by frangibly connecting the support bracket 500 to the vehicle using one or more frangible connectors in the form of shaped blocks called capsules 400. In a crash the forces on the bracket are sufficiently high to cause the bracket to break away from the capsules thus permitting the bracket to move relative to the vehicle.
A possible problem with this prior art arrangement is that if the clamp mechanism 300 is unlocked and an axial adjustment force F is applied to the steering column that is too high, it could cause the telescopic shroud to reach the end of its adjustment range with such a force that the capsules that fix the bracket to the vehicle body are damaged or even sheared. This is because the force load path is directly transferred to the connectors at extremes of travel. This would render the column partially or fully disengaged from the vehicle.